The present invention relates generally to the field of magnetic data storage and retrieval. In particular, the present invention relates to a high frequency writer having a composite core structure.
A typical magnetic transducing head consists of two portions: a writer portion for storing magnetically-encoded information on a magnetic disc and a reader portion for retrieving that magnetically-encoded information from the disc. The reader typically consists of two shields and a magnetoresistive (MR) sensor positioned between the shields. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
The writer typically consists of two magnetic poles, or a magnetic core, separated from each other at an air bearing surface of the write head by a write gap and connected to each other at a region away from the air bearing surface by a back via. Positioned between the two poles are one or more layers of conductive coils encapsulated by insulating layers. The writer and the reader are often arranged in a merged configuration in which a shared pole serves as both a shield in the reader and a magnetic pole in the writer.
To write data to the magnetic media, a time-varying electrical current, or write current, is caused to flow through the conductive coils. The write current produces a time-varying magnetic field in the magnetic poles. The magnetic field bridges the write gap forming a write gap field. The magnetic media is passed over the air bearing surface of the writer at a predetermined distance such that the magnetic surface of the media passes through the gap field. As the write current changes, the write gap field changes in intensity and direction.
Recent years have seen considerable demand for ever increasing data storage densities. Generally, the data storage capacity of a magnetic data storage and retrieval device is increased through use of a magnetic media supporting an increased areal density, which is the number of units of data stored in a unit area of the media. Areal density is determined by two components of the magnetic media: the track density (the number of data tracks per unit width of the magnetic media) and the linear density (the number of units of data stored per unit length of a data track). To increase the areal density of a magnetic media, one must increase the linear density and/or the track density of the magnetic media.
Increases in areal density have been achieved by increasing the strength of the write gap field, decreasing the thickness of the gap between the magnetic poles at the air bearing surface, decreasing the width of the writer poles at the air bearing surface and increasing the coercivity of the magnetic media. These improvements require the magnetic core be formed of a high magnetic moment material.
Recent years have also seen considerable demand for ever increasing data rates. Generally, the data rate of a writer is increased by minimizing the occurrence of eddy currents through the magnetic core. Eddy currents are induced through the magnetic core each time the write gap field changes directions. These eddy currents, which are a counteracting flow of current to the change in direction of the write gap field, have a negative effect on the performance of the transducing head. First, the eddy currents act as a shield to prevent external fields from penetrating the magnetic core, thereby reducing the efficiency of the transducing head. Second, the increased eddy currents increase the time required to reverse the direction of magnetic flux through the magnetic core, thereby negatively impacting the data rate of the writer.
Eddy current effects can be reduced by increasing the resistivity of the material forming the magnetic core. Higher resistivity materials, however, generally have lower saturation moments; but, as discussed above, higher magnetic moment materials are needed to achieve higher data storage densities.
Eddy current effects can also be reduced by forming the core of horizontal laminations of thin films which alternate between thin films of traditional core materials and thin films of electrically insulating materials. However, the choice of a lamination for the core will increase manufacturing costs since sputtering, rather than plating, technology generally must be employed for the deposit of traditional core materials on electrically insulating materials. Additionally, the use of a laminate core will necessarily have a reduced magnetic moment, and consequently, a lower data storage density.
Since it is difficult to find a material having both a high magnetic moment and a high resistivity, more recent prior art writers have used multiple materials to lend both these properties to the writer. One such prior art approach is to form the magnetic core of two layers, one of which is formed of a high magnetic moment material and the other of which is formed of a high resistivity material. But, the use of a multi-layer core will necessarily reduce the overall magnetic moment over that possible with a writer formed of solely the high magnetic moment material.
A second prior art approach is to form a top pole of the magnetic core of two pieces: one of a high magnetic moment material and a second of a high resistivity material. This xe2x80x9ctwo piece polexe2x80x9d (TPP) design originated from the need to build the pole tip separately from the pole yoke due to photo-processing concerns. Additionally, a bottom pole of the magnetic core may be a recessed pole similarly formed of two pieces. In the case in which both the top and bottom pole are formed of two pieces, the build process of the writer would progress as follows: A planar second bottom pole piece would be deposited; a planar first bottom pole piece would be deposited on a portion of the second bottom pole piece; a write gap layer would be deposited over an exposed portion of the second bottom pole piece and the first bottom pole piece, a planar first top pole piece would be deposited over the write gap layer; a tri-layer stack formed of the first bottom pole piece, the write gap layer, and the first top pole piece would be shaped to define a pole tip region; insulating layers and coils would be deposited; and finally, a second top pole piece would be deposited over the first top pole piece, as well as the insulating layers and coils.
This build process is necessary because the first bottom pole piece and the second bottom pole piece need to be built on a flat surface to allow for proper shaping of the pole tips. Thus, the existing TPP structures all require stacking the first pole piece on the second pole piece, which is inefficient for flux transportation.
Accordingly, there is need for a high efficiency writer core capable of both high magnetic data storage densities and data rates.
The present invention is a high efficiency recording head having a composite core which enables the writer to produce increased write gap fields while minimizing eddy current therein, thus enabling the writer to have increased data storage densities and data rates.
A magnetic transducing head of the present invention has a bottom shield, a shared pole, a read element, a substantially planar composite top pole; and a conductive coil. The read element is positioned between the bottom shield and the shared pole. The top pole is formed of high magnetic moment pole tip portion and a high resistivity yoke portion. The pole tip portion of the top pole is substantially coplanar with the yoke portion of the top pole. The pole tip portion of the top pole is separated from the shared pole at an air bearing surface of the transducing head by a write gap, while the yoke portion of the top pole is in contact with the shared pole opposite the air bearing surface. At least a portion of the conductive coil is positioned between the shared pole and the top pole.
In a preferred embodiment of the present invention, the shared pole of the magnetic transducing head is a multi-part structure formed of a substantially planar yoke portion, a pole tip portion positioned on the yoke portion adjacent the air bearing surface and a back via portion positioned on the yoke portion opposite the air bearing surface such that a U-shaped cavity is formed above the yoke portion between the pole tip and the back via portions. A thickness of the back via portion is preferably greater than a thickness of the pole tip portion so that the back via portion is in contact with the top pole while the pole tip portion is separated from the top pole by the write gap.